This method is for the gravimetric determination of the water vapor transmission rate (WVTR) of sheet materials at 37.8 degrees C (100 degrees F) with an atmosphere of 90% RH on one side and a desiccant on the other.

It is generally suitable for any material up to 3 mm (1/8 in.) thick, although it may be used with caution for thicker materials if the edges of the specimen are completely sealed.

For testing at other conditions see TAPPI T 448 Water Vapor Transmission Rate of Paper and Paperboard at 23 degrees C (73 degrees F) and at 50% RH.

This test can be used for both creased and uncreased specimens. See TAPPI T 465 Static Creasing of Paper for WVT Tests or TAPPI UM 590 Creasing of Paperboard for Water Vapor Transmission Rate (WVTR) Testing.